Developing device for electrostatic images



April 14, 1953 E. R. SABEL EIAL 2,635,046 DEVELOPING DEVICE FORELECTROSTATIC IMAGES Filed Sept. 2, 1950 5 Sheets-Sheet l Fig.3

uvvzzvroxs non/41o a. an. CLYDL R. MAYO MW ATTORNEYS 5 Y L a 6 2 mi N 4TB 0 a M m 5 m J .r 3 WR T 5 DR A 2 m R: m .A H S MY 3 E M N F E. R.SABEL ETAL DEVELOPING DEVICE FOR ELECTROSTATIC IMAGES April 14, 1953Flled Sept 2, 1950 beads. 'justed in relation to the resin powder thatthe carrier imparts to the powder particles electro- Patentecl Apr. 14,1953 DEVELOPING DEVICE FOR ELECTROSTATIC IMAGES Edward R. Sahel andClyde R. Mayo, Rochester,

N. Y., assignors to The Haloicl Company, Rochester, N. Y., a corporationof New York Application September 2, 1950, Serial N o. 182,958

5 Claims.

This invention relates to developing devices,

and particularly to devices for applying powder to electrostatic images,such as images on electrophotographic plates and the like.

In the process of electrophotography, or xerography, an electrostaticlatent image is obtained 'upon an insulating image layer, such as alayer of photoconductive insulating material supported on a conductivebacking. For example, the photoconductive insulating layer may be givena uniform electrostatic charge over its surface and then exposed to alight image to discharge the portions of the layer exposed to lightwhile leaving the electrostatic charges remaining in the dark areas. Theimage may then be developed by depositing a finely-divided material onthe charged areas. Thus, a fine powder may be sprinkled or cascaded overthe plate and the excess allowed to pass off the plate leaving thepowfused onto a bare metal plate or one produced by Writing on the platewith an insulating ink,

consisting of an insulating material dissolved in a volatile vehicle.Such plates may be used to produce powder images by passing the platesunder a corona discharge electrode to deposit ele trostatic charges onthe insulating image and then dusting the plate to produce a powderimage.

According to one method of developing the electrostatic image plates, adeveloper is used comprising a finely-divided, pigmented resin powdermixed with a granular carrier material such as certain crystalline saltsor resin-coated glass The composition of the carrier is so adstaticcharges opposite in polarity to the charges on the electrostatic imagewhich it is desired to develop. It has been found that images canreadily be developed with such compositions by cascading them over thesurface of the electrostatic image plate. One apparatus for doing thiscomprises a tilting tray in which the plate is placed with its faceupward, and a charge of tions such as a charge of finely-dividedpigmented powder without a carrier may sometimes also be used with thisdeveloping apparatus.

While uniform development can be achieved by using a tilting tray it hasbeen found that the speed at which the tray is tilted has a considerableeifect upon the quality of results obtained. As a result some experienceis required in order to acquire the necessary skill to produce perfectpowder images by this arrangement.

The present invention contemplates an improvement in devices forcascading developing powders over electrostatic image plates wherein anautomatic metering arrangement is provided to control the rate of powderdischarge across the plate surface. In one of its specific embodimentsthe invention contemplates a tilting developing tray provided withpowder reservoirs arranged at the ends and moving gate arrangements forrestricting the rate of powder discharge from the reservoirs when thetray is tilted to cascade powder over a plate and to open to freelyadmit developer when it is returned to the reservoirs.

The invention comprises the features of construction, combination ofelements, arrangement of parts, and methods of operation referred toabove or which will be brought out and exemplified in the disclosurehereinafter set forth,

including the illustrations in the drawing.

In the drawings:

Figure 1 is a side elevation of a developing device embodying featuresof the present inven tion;

Figure 2 is a vertical section of part of said device;

Figure 3 is a section on the line 33 of Figure 1;

Figure 4 is a vertical section through a modified developing tray. and

Figure 5 is a section on the line '5-5 of Figure 4.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the constructionand arrangement of parts and in the method of operation withoutdeparting from the spirit of the invention. In the following descriptionand in the claims parts will be identified by specific names forconvenience, but they are intended to be as generic in their application'to similar parts as the art will permit.

Referring to Figures 1, 2 and 3, the developing device illustratedcomprises a stationary base I!) which may comprise a pair of uprights li eX- tending up in spaced parallel relation from a base plate !'2adapted to rest upon surface of a table or other support. Uprights H andbase plate l2 may be formed of wood, for example, and the uprights maybe provided with a mounting plate l3 of metal, such as brass, on theirouter faces near their upper ends, in which are provided bushings i i inwhich the axle pins [5 of a tilting tray it are pinioned.

Tray [6 may comprise a flat bottom wall I! to which are attached endwalls It and side walls I 9 to provide a shallow tray. A pair of topwalls 20 enclose the two ends of the tray to provide powder reservoirsat the ends, while leaving the central area of the tray exposed; Fourlocating pins 2! are mounted in spaced relation on bottom I? to positionan electrostatic image plate 22 in the center of the bottom of the tray,for purposes of development. These pins are located close to side wallsH9 in order to avoid disturbing the flow of powder over the image area.

A pair of metering gates 24' are provided-between the ends of plate 22and the powder reservoirs. Each gate 2 5 may" comprise a sheet metalplate mounted on a pair of cast ribs 25 drilled to receive a pivot shaft26 pivoted in the side walls 19 of the tray. A setscrew 21- is threadedinto each casting 25 to lock the-part to the shaft. Sheet metal gates 26are secured to cast ribs 25 by setscrews 28 which pass through mountingslots 29 in the sheet metal gatemembers. It is thus possible byloosening setscrews 28 to adjust the gap or metering opening between thelower edge of gate members 24 and-the bottom ll of the tray. The gateposition is adjusted to give the desired rate of developer flow acrossthe plate when the tray is tilted to its maximum angle, which may be,for example, 30 above the horizontal.

I l in which the tray is pivoted. The free ends of the connecting rodsare pivoted, respectively,

on pivot pins 38 on the swinging arms of bell crank levers 39. Therelative angular positions of levers 3G and gates 24 on their shaftsare. adjusted to bring gate 24 perpendicular to the bottom ll of thetray when its respective tray end is tilted to uppermost position asshown for the right-hand gate in Figures 1 and 2. The. gate therebyrestricts the rate of flow of developer powder 23 over the plate, theamount being'determined by the metering gap providedbetween the loweredge of gate 24 and the bottom ll of the tray. The length of cranklevers 3i], connecting rods 3! and the distance from the axle [5 of thetray to pivot pin 32 of the connecting rods are so proportioned inrelation to each other that when an end of the tray reaches itslowermost position the gate 24 at that end is swung open by connectingrod 3! acting through crank lever 39 to bring the gate 24 completely outof the path of developing powder passing downward over the plate, asshown for the left-hand gate in Figures 1 and 2.. In order to permitadjustment of the effective lengths of connecting rods 31 they arethreaded into their end blocks.

With a charge of developing. powder 23 placed in one end of the tray andan electrostatic image plate 22 positioned between stop pins 2!, thetray may be tilted to the left and right so that the developer will passback and forth over the surface of the plate and some of it will bedeposited on the electrostatic image to develop the image. During thetilting of the tray the swinging metering gates 24 are moved by thelever mechanism into and out of metering position to control the rate offlow of powder over the plate without the necessity. of skillful controlby the operator; The gates are moved out of the path of the descendingpowder to avoid interference or obstruction of flow as it passes oii theplate into an end chamber. In operation, the developing powder willbegin to flow out over the plate shortly before the tray reaches theextreme of itstilted position. However, the lever arrangement is suchthat gate will be substantially in the same metering position through asmall angle oitravel of the tray. This is effected by virtue of the factthat the connecting rod 3| is nearing dead center position with respectto pivot 32 at this time.

Easy removal. of plate 22. after ittxhas. beenade veloped. is madepossible by a plunger 33mounted bottom wall 11.1 The plunger comprises asliding pin having a cap-:34 adapted to: be. :engaged by thehand of. theuser. The pin is arranged to slide in aligned openings in bottom I"!and. in the end of a tube 35 secured to bottom. I! andcontaining a coilspring 36 to'retract. .the plunger by pressure against a flange" 31provided on the" plunger.

It will be evident thatv an improved developing tray has been providedin which the minimum of skill is required on the part of the operator tocontrol the rate of flow of developing powder and that an automaticcontrol means is provided in'which the rate. of development issubstantially uniform and independent of operators-judgment.The-advantage of the invention will be further appreciated when it isconsidered that developing of sensitive electrophotographic plates must.be carried on in a. darkroom where the operator is unable to see clearlythe operations being performed Figures 4 and 5 illustrate adevelopingtray 40 which. does not require darkroom. operation but inwhich the developing operation cannot be-observed. by the operator. Thisdeveloping tray is provided with metering means to predetermine the rateof flow of developing powder.

Tray 30 comprises a bottom wall 4!, end walls .42, side-walls 43. and asolid top wall 44. Bottom wall ll is provided with a central opening. orwindow and the-edges of wall. 4| defining the two ends of the window arebent outward at a slight angle at to provide a beveled portion at eachend of the window. A tapered rubber blade 46 is mounted, by means of aslot extending into its rear edge on the edge of each beveled portion45;.the rubber blade tapering to a sharpfflexi ble edge terminatingslightly below the plane of bottom 4! because of the bevel angle. Stripsof sponge rubber i! are cemented to the face. of

bottom wall 4! along the two edges of the win- "ac-snore holder '50."It'i'vill'als'o'be apparent that the plate holder is provided with-asuitable slide slot to permit insertion of a light slide over the plateto protet it fr'oin light "while it is being transferred from exposureposition to the developing tra 40. Theplate can be readily placed inposition on the tray and the light slide removed Without danger ofexposing the plate "to light, clamping being completed after the shieldis removed.

The tray 40 is provided with a pair of short aligned pivot shafts 52secured to the middle of side walls 43 to permit tilting on a suitablesup port such as a pair of parallel arms 53 provided with U-shapedreceptacles 54 in their ends in which shaft 52 can be received. Arms 53may comprise part of a telescoping slide adapted to enable withdrawaland return of tray 49 into a drawer space or recess. Tray 40 can, ofcourse, also be mounted on a base such as base of Figure 1.

Tray is provided with swinging gates 55 between each of the tray endsand beveled portion 45. Each gate 55 may comprise a sheet metal stripbent over a longitudinal axis into a V-shape with one leg longer thanthe other. The gate is secured as by welding to a shaft 56 mountedhorizontally between bushings 5'! (Figure 5) in the side walls 43 sothat gate 55 swings freely on its pivot. A washer 58 is provided at eachend inside walls 43 to prevent jamming. The short arm 59 of the swinginggate member is provided with a relatively heavy ballast weight such as ametal bar which is welded along the edge of portion 59 and stop pins 5!are provided in side walls 43 in such position as to limit the swing ofgate member in one direction to stop the gate when it is substantiallyperpendicular to bottom wall 4| of the tray as shown for the upper endof the tray in Figure 4. In this position the free edge of gate 55 isspaced slight- In operation the tray is prepared for use by turning itabout its pivot 52 to bring bottom wall 4| to top position and a chargeof developing powder is poured into the tray. An electrostatic imageplate 49 in a suitable frame is then clamped over the window in wall 4!by spring clips 48 and the tray is swung about its pivots to bring wall4| and the plate to the underside of the tray. During this operation thedeveloping powder accumulates in the lower end of the tray. As therotation of the tray is continued through horizontal position and theonce lower end is raised to an angle of 30 or so above the horizontal,gate 55 swings to a position in which its arm 59 is against stops BI andshortly thereafter developing powder 23 collects above the gate asshown, for example, in Figure 4 and begins to flow through the opening62 at a predetermined rate. The powder cascades over the surface ofplate 49 developing the electrostatic image and flows off the lower edgeof the plate into the end 6 of thetray. Durin'g'this operation gate 55,which is at the lower end of the tray, is swung back to substantiallyopen position by counterweight "53 thus permitting 'free access ofdeveloping powder into the reservoir at the end of the tray.

It will be "evident that this developing tray arrangement provides foraccurate and automatic inete'r'ing of development powder duringdevelopment and enables the operator to obtain uniform results eventhough the developing procedure can not be observed.

While the present "invention, as to its objects and advantages, has beendescribed herein as carried out in'sp'ecific'embodiments thereof, it isnot desired to be limited thereby but it'is intended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A device for developing electrostatic images on image plates,comprising, in combination, a tilting support for an image plate tosupport said plate face upward and tilt said plate from one inclinedposition in which one end is uppermost to the opposite inclined positionin which the other end is uppermost, a reservoir for developing powderon said tilting support beyond one end of said plate to discharge powderonto said piate when said reservoir is above said plate and to receivepowder passing off said plate when said reservoir is below said plate, amovable metering gate between said reservoir and said plate which gatein its fully closed position defines a restricted metering opening fromsaid reservoir to said plate, and control means to open said gate toadmit powder to said reservoir when said reservoir is below said plateand to close said gate to its metering position to restrict the rate offlow of powder out of said reservoir onto plate when said reservoir isabove said plate.

2. A device as claimed in claim 1 in which said control means isresponsive to the position of said tilting support.

3. A developing device for electrostatic image plates, comprising, incombination, a support, a developing tray pivoted thereon for tiltingabout a horizontal axis from an inclined position in which a first endis uppermost through horizontal position to a second inclined positionin which the second end is uppermost, said tray comprising side and endwalls and a bottom wall, locating means for positioning an electrostaticimage plate on said bottom wall between the ends of said tray, swinginggates pivoted on horizontal axes on said tray between the ends of saidplate and the ends of said tray respectively which gates in their fullyclosed positions define restricted metering openings from saidreservoirs to said plate, and a mechanical interlock between each ofsaid gates and said support for swinging each gate open when itsrespective end of said tray is lowered, and for swinging each gateclosed to the predetermined metering gap when its respective end of saidtray is raised.

4. A device for developing electrostatic images comprising, incombination, a base, a tilting tray pivoted about a horizontal axis onsaid base plate locating means on said tray for positioning a plate inthe bottom of said tray between the ends thereof, the ends of said trayproviding powder reservoirs for receiving and discharging powder oversaid plate, a swinging gate pivoted on an axis extending across saidtray between each of said reservoirs and the respective ends of saidplate, a crank lever on each of said gates and connecting rods betweensaid crank levers and a pin on said base eccentric to said horizontalaxis to open and close said gates respectively respon- 'sive to thetilting of said tray on said horizontal axis, said gates being openedwhen in lower position and closed when in upper position.

5. A developing tray for electrostatic image plates, said traycomprising side and end walls and a bottom wall, pivots for tilting saidtray about a horizontal axis from an inclined position in which a firstend is uppermost through horizontal position to a second inclinedposition in which the second end isuppermost, locating means forpositioning an electrostatic image plate on said bottom wall between theends of said tray, swinging gates pivoted on horizontal axes on saidtray between the ends of said plate and the ends of said trayrespectively which gates References Cited in the file of this patent:UNITED STATES PATENTS Number Name Date 661,080 Sackett Nov. 6, 19002,550,724 Sabel et a1 May 1, 1951 2,550,738

Walkup May 1,' 1951

1. A DEVICE FOR DEVELOPING ELECTROSTATIC IMAGES ON IMAGES PLATES,COMPRISING, IN COMBINATION, A TILTING SUPPORT FOR AN IMAGE PLATE TOSUPPORT SAID PLATE FACE UPWARD AND TILT SAID PLATE FROM ONE INCLINEDPOSITION IN WHICH ONE END IS UPPERMOST TO THE OPPOSITE INCLINED POSITIONIN WHICH THE OTHER END IS UPPERMOST, A RESERVOIR FOR DEVELOPING POWDERON SAID TILTING SUPPORT BEYOND ONE END OF SAID PLATE TO DISCHARGE POWDERONTO SAID PLATE WHEN SAID RESERVIOR IS ABOVE SAID PLATE AND TO RECEIVEPOWDER PASSING OFF SAID PLATE WHEN SAID RESERVOIR IS BELOW SAID PLATE, AMOVABLE METERING GATE BETWEEN SAID RESERVOIR AND SAID PLATE WHICH GATEIN ITS FULLY CLOSED POSITION DEFINES A RESTRICTED METERING OPENING FROMSAID RESERVOIR TO SAID PLATE, AND CONTROL MEANS TO OPEN SAID GATE TOADMIT POWDER TO SAID RESERVOIR WHEN SAID RESERVOIR IS BELOW SAID PLATEAND TO CLOSE SAID GATE TO ITS METERING POSITION TO RESTRICT THE RATE OFFLOW OF POWDER OUT OF SAID RESEROIR ONTO SAID PLATE WHEN SAID RESERVOIRIS ABOVE SAID PLATE.